It’s easy to see why Steve Hackett found fault with The Sum of the Parts, released this week via Eagle Rock. Mainly, because there are so many parts missing in its second half.

The documentary, directed by John Edginton, has no problem setting things up. As Genesis’ earliest years unfold, a lineup featuring Mike Rutherford and Anthony Phillips is eventually completed with the addition of Tony Banks and his friend Peter Gabriel to form the group’s initial incarnation. Later, with Phillips’ exit, things gain momentum with the arrival of both Phil Collins and Steve Hackett.

Really, through the moment in which Peter Gabriel splits with Genesis, The Sum of the Parts does a fine job. Even Phillips, a critical figure who is often unjustly forgotten today, gets his share of attention. Interview scenes that find Banks, Collins, Gabriel, Hackett and Rutherford in the same room do much to shed light on Genesis’ working dynamic back then — and today. (Gabriel, for instance, is still shyly honest; Collins is the jokester; Banks is the typically overlooked taskmaster — while Hackett remains ever apart.) Then, as the guitarist makes a frank expression of his own growing restlessness in the band dynamic, Hackett suddenly disappears from The Sum of the Parts.

His two concluding years in Genesis — featuring a pair of terrific studio efforts (both of them Top 10 smashes in the U.K., and Top 40 hits stateside, by the way), a slew of fan favorites like “Eleventh Earl of Mar,” “Ripples,” “Dance on a Volcano” and “Your Own Special Way,” plus a Top 5 UK live album — are somehow explained away in a matter of moments. This was, remember, a pivotal member going back a total of six studio efforts, the last four of which were Genesis’ first-ever gold sellers in the U.S.

Insult then follows injury when The Sum of the Parts rushes toward their subsequent solo efforts. Peter Gabriel’s early career is afforded an incomplete and confusing overview, while Mike Rutherford’s hitmaking era with Mike and the Mechanics breezes past their initial breakthrough album. Most confusing of all, however, is how The Sum of the Parts handles Steve Hackett — who is somehow given less screen time than Tony Banks.

Hackett, after all, scored a Top 20 UK hit with his solo debut, 1975’s Voyage of the Acolyte — which featured both Mike Rutherford and Phil Collins. By 1983, he’d strung together six Top 40 UK albums, including the No. 9 1980 favorite Defector. As a member of GTR with Yes’ Steve Howe, Hackett added a self-titled No. 11 Billboard hit album, as well as a Top 20 single with “When the Heart Rules the Mind.” He then reached No. 24 in the UK with 2012’s Genesis Revisited II.

Meanwhile, Banks — whatever his influence on Genesis itself — has had the least recognizable, least decorated solo career of any of the five classic-era members. He’s only had two albums reach his home country’s charts, highlighted by A Curious Feeling — a No. 21 finisher in the UK back in ’79. By 1995, Tony Banks’ Strictly Inc. wasn’t even released in America. Billboard rightly notes that “none of his attempts have been very commercially successful.” Not that The Sum of the Parts noticed.

Then, there’s poor Ray Wilson, who stepped in after Phil Collins retired for an underrated late-1990s turn fronting Genesis. He’s not featured in The Sum of the Parts at all. Is it any surprise that Wilson has taken to appearing with Steve Hackett on stage? If nothing else, they must share a bitter sense of rejection from the band they both gave so much to.